1. Field of the Invention
The present invention relates to a fastener driving tool provided with an improved nail head guide surface of an exit port from which nails are struck out.
2. Background Art
A related art fastener driving tool will be described by using FIGS. 6 to 10.
The loading of nails 2, which are joined together substantially in parallel with one another at equal intervals by a connecting member made of paper, a plastic material and the like, into a magazine is done from a nail loading port opened in a rear end wall of the magazine 3.
The shape of a cross section of the magazine 3 taken in the direction which is at right angles to the direction in which the nail 2 is supplied is as shown in FIG. 6, so as to retain the nail 2.
In an upper portion of FIG. 6, an upper side of a nail head 2a is held on an upper surface 5a of a guide groove 5. In a lower portion of the same drawing, a lower side of the nail head 2b is held on both sides of a lower surface 5b of the guide groove 5. In a lateral direction of the nail 2, an upper portion of the nail 2 is held on guides 6 immediately under the lower surface 5b, while a shank portion of the nail 2 is held on guides 7 provided in a substantially central portion of the magazine 3.
The magazine 3 is provided at two vertically spaced portions thereof with guide walls 42 adapted to guide a nail feed mechanism 8 so that the nail feed mechanism 8 is moved slidingly toward an exit portion 9. The nail feed mechanism 8 includes a feeder spring 12 having a rotary shaft 11, which extends in the direction which is at right angles to the shank 2b of the nail 2, so as to press the nail 2 toward the exit portion 9, and a nail feeder 14 adapted to press the nail 2 directly, and be turned around a rotary shaft 13 from the guide groove 5 by the loaded nail 2 when the nail feed mechanism 8 is drawn up backward toward the nail loading port 4 after the nail 2 is loaded onto the magazine 3 from the nail loading port 4 at a rear end of the magazine 3, and project into the guide groove 5 by a pressing force of a spring 43 when the nail feed mechanism gets over the nail 2.
The magazine 3 is extrusion molded out of a light non-ferrous metal, such as aluminum and magnesium. Since both sides of the guide groove 5 through which a nail head 2a passes are readily worm out, an iron rail 15 is inserted in an inner side of the magazine 3.
In a nose 16, a flat guide surface 10 for guiding a head 17a of a first nail 17 is provided, and this guide surface 10 is made of a gentle, inclined surface 20 and joined to an inner circumference of an exit port 19 so as to allow the head 17a of the first nail 17 to enter the exit port 19 while the mentioned nail head 17a is struck into a wooden material 18. The guide surface 10 is provided so as to determine a position of the first nail 17, i.e. a second nail 21 so that the second nail 21 is not struck by a lower end surface 22a of a driver blade 22. When the second nail 21 should also be struck, both the first nail 27 and second nail 21 are struck, so that the nails cannot be struck out from the exit port 19 since a diameter of the exit port is equal to that of one nail, consequently, there is the possibility that the exit port is clogged with the two nails.
The exit port 19 is formed to such a minimum size within the scope of the specifications that permits a nail head 2a of a maximum diameter to enter the same so that the nail 2 is rarely bent and buckled due to a load imparted thereto when the nail is struck into the wooden material 18.
A cross section of the driver blade 22 has a maximum substantially recessed shape capable of being moved slidingly in the exit port 19 which shunts the guide surface 10 so as to prevent the bending and buckling of the driver blade 22 and the abrasion of the free end surfaces 22a. There is a driver blade the free end surfaces 22a of which are chamfered gently and additionally within the scope of the specification so that two nails even having nail heads 2a of a small diameter are not struck at a time.
A nail striking operation carried out by the fastener driving tool 1 of the above-mentioned structure will be described with reference to FIGS. 6 to 8. The compressed air supplied to the fastener driving tool by connecting an air hose (not shown) to a body of the fastener driving tool 1 is stored in a pressure accumulation chamber 24.
When a trigger valve 27 is turned on by carrying out both the drawing of a trigger 25 and the applying of a push lever 26 to the wooden material 18, a main valve 28 is moved toward an upper dead center, the pressure accumulation chamber 24 and an upper side of a piston 30 in the cylinder 29 communicate with each other, and the pressure accumulation chamber 24 and an air passage 31 are shut off from each other. The piston 30 is moved quickly toward a lower dead point by the compressed air flowing from the pressure accumulation chamber 24 into the upper side of the piston 30 in the cylinder 29, the nail 2 is struck into the wooden material 18 by the driver blade 22 fixed to the piston 30 in one united body. When the air on the lower side of the piston 30 in the cylinder 29 is returned to a return air chamber 33 via the air passage 32 with the piston 30 passing through an air passage 35 provided with a check valve 34, a part of the compressed air on the upper side of the piston 30 flows into the return air chamber 33 via the air passage 35. The piston 30 contacts a piston bumper 36 in the lower dead center, and the piston bumper 36 is deformed to absorb the excess energy of the piston 30. When the trigger valve 27 is turned off by returning the trigger 25 or by stopping the applying of the push lever 26 to the wooden material 18, the main valve 28 is moved toward the lower dead center. The main valve 28 is closed, and the pressure accumulation chamber 24 and the upper side of the piston 30 in the cylinder 29 are shut off from each other, the upper side of the piston 30 in the cylinder 29 and the atmospheric air being communicated with each other by an exhaust valve rubber 37. The lower side of the piston 30 is pressed by the compressed air accumulated in the return air chamber 33, and the piston 30 is moved quickly toward the upper dead center. The compressed air on the upper side of the piston 30 is discharged from an exhaust hole 39 to the atmospheric air via the air passage 31, air passage 31 and an expansion chamber 38, and the fastener driving tool is returned to an initial condition. When this process is carried out repeatedly, the connected nails 2 are struck into the wooden material 18 successively.
A structure for guiding a first nail by a guide surface 10′ of another construction will now be shown in FIG. 9 to FIG. 10. A head 17a of the first nail 17 is guided in an exit port 19, and a groove 40 for guiding a lower shank end 17b of the first nail 17 is provided at the portion of the magazine 3 which is on the opposite side of the exit port 19. The groove 40 is so wide as to permit the shank 17c of the nail to be held therein but not so wide as to permit the nail head 17a to be held therein.
A cross-section of the driver blade 22′ is not of such a recessed shape that shunts the guide surface 10 shown in FIG. 7 but is of a substantially semicircular shape. The diameter of the nail head 2a is set slightly smaller than that of the exit port 19. The free end surfaces 22a′ of the driver blade 22′ are provided with chamfered portions 23′ larger than those of the structure of FIG. 7 and FIG. 8 so that the free end surfaces 22a′ do not strike the second nail 21.
[Patent Document 1] JP-A-63-174881
[Patent Document 2] JP-A-2001-54880
In general, the outer circumference of a nail head 2a is circular. The guide surface 10 of a nose of a related art fastener driving tool is a flat surface. Therefore, when the nail 2 pressed by the nail feeder 8, the nail head 2a impinges upon the guide surface 10 at one point only thereon, so that the guide surface 10 is worn with ease locally. When the abrasion of the guide surface progresses, the nail head 17a of the first nail 17 advances into the worn guide surface 10a, and the second nail 21 further advances into the exit port 19 as shown in FIG. 8. The second nail 21 then gets over the chamfered portion 23 provided on the driver blade 22 to cause the superposition 41 of the second nail 21 on the chamfered portion 23 to occur. As a result, the free end surfaces 22a of the driver blade 22 strike both the first nail and second nail 21 to cause the stoppage of these nails to occur.
In the structure of FIG. 9 to FIG. 10, the wear on the guide surface 10′ caused by the contact of the nail head therewith does not have a problem. Since the guide surface 10′ does not project into the exit port 19, it is necessary that a large chamfered portion 23′ be provided so as to prevent the free end surfaces 22a from striking the second nail. As a result, the areas of the free end surfaces become small to cause the driver blade 22′ to be damaged due to the wear on and the excessively large surface pressure on the guide surface.